Transient receptor potential vanilloid 4 mediates protease activated receptor 2-induced sensitization of colonic afferent nerves and visceral hyperalgesia

Abstract

Protease-activated receptor (PAR(2)) is expressed by nociceptive neurons and activated during inflammation by proteases from mast cells, the intestinal lumen, and the circulation. Agonists of PAR(2) cause hyperexcitability of intestinal sensory neurons and hyperalgesia to distensive stimuli by unknown mechanisms. We evaluated the role of the transient receptor potential vanilloid 4 (TRPV4) in PAR(2)-induced mechanical hyperalgesia of the mouse colon. Colonic sensory neurons, identified by retrograde tracing, expressed immunoreactive TRPV4, PAR(2), and calcitonin gene-related peptide and are thus implicated in nociception. To assess nociception, visceromotor responses (VMR) to colorectal distension (CRD) were measured by electromyography of abdominal muscles. In TRPV4(+/+) mice, intraluminal PAR(2) activating peptide (PAR(2)-AP) exacerbated VMR to graded CRD from 6-24 h, indicative of mechanical hyperalgesia. PAR(2)-induced hyperalgesia was not observed in TRPV4(-/-) mice. PAR(2)-AP evoked discharge of action potentials from colonic afferent neurons in TRPV4(+/+) mice, but not from TRPV4(-/-) mice. The TRPV4 agonists 5',6'-epoxyeicosatrienoic acid and 4alpha-phorbol 12,13-didecanoate stimulated discharge of action potentials in colonic afferent fibers and enhanced current responses recorded from retrogradely labeled colonic dorsal root ganglia neurons, confirming expression of functional TRPV4. PAR(2)-AP enhanced these responses, indicating sensitization of TRPV4. Thus TRPV4 is expressed by primary spinal afferent neurons innervating the colon. Activation of PAR(2) increases currents in these neurons, evokes discharge of action potentials from colonic afferent fibers, and induces mechanical hyperalgesia. These responses require the presence of functional TRPV4. Therefore, TRPV4 is required for PAR(2)-induced mechanical hyperalgesia and excitation of colonic afferent neurons.

TRP channels in neurogastroenterology: opportunities for therapeutic intervention

“…In agreement, Cenac et al and Sipe et al furthermore showed that PAR2-induced hypersensitivity is mediated by the activation of TRPV4 (Cenac et al, 2008;Sipe et al, 2008). TRPV4 and PAR2 are co-expressed on the majority of spinal afferents innervating the murine colon and TRPV4 deletion or antagonism completely abolishes the sensitizing effects of PAR2 activation in these neurons (Sipe et al, 2008). However, because PAR2-induced Ca 2+ transients were not inhibited by TRPV4-targeted siRNA in DRG neurons, parallel, yet incremental, pathways for PAR2 and TRPV4 are suggested at the cellular level (Cenac et al, 2008).…”

“…In agreement, Cenac et al and Sipe et al furthermore showed that PAR2-induced hypersensitivity is mediated by the activation of TRPV4 (Cenac et al, 2008;Sipe et al, 2008). TRPV4 and PAR2 are co-expressed on the majority of spinal afferents innervating the murine colon and TRPV4 deletion or antagonism completely abolishes the sensitizing effects of PAR2 activation in these neurons (Sipe et al, 2008).…”

Extrinsic primary afferent signalling in the gut

“…124 Activation of PAR2, by proteases released by mast cell degranulation, can lead to behavioural hypersensitivity and increased afferent firing via sensitization of TRPV4. 123,125 TRPA1 is the third TRP channel known to have a key role in setting the sensitivity of vascular afferents. It might also mediate PAR2-evoked sensitization in the gut 126 and/or bradykininmediated hypersensitivity.…”

Cathepsin S Causes Inflammatory Pain via Biased Agonism of PAR2 and TRPV4

“…Cat-S is also activated in inflammatory diseases including rheumatoid arthritis (4) and colitis (5). Given the established contributions of PAR 2 and TRPV4 to arthritis (63) and colitis (30,64,65), antagonists of Cat-S, PAR 2 , and TRPV4 may be valuable treatments for these and other inflammatory diseases.…”